what's the difference between Blue-Ray DVDs and HDDVDs?

Answer 1

Both Blu Ray and HD DVD use blue laser, but Blu Ray uses a narrower-beam laser, so it has higher capacity.
There are some other differences in formats, navigations and copy protection

Check
http://en.wikipedia.org/wiki/Blu-ray_Disc

Answer 2

I think blue rays usea a blue laser and a dvd uses a red laser.

Answer 3

i know one difference is blue ray are smaller discs and are supposedly even better quality than the hd dvds.. and blue ray cost more too..